1. Field of the Invention
This invention relates to a method and apparatus designed for inspecting translucent containers for the presence of extraneous matter and/or cracks. The invention is particularly suitable for use with translucent containers when the colored density and/or wall thickness of the translucent containers vary significantly from container to container.
2. Description of the Prior Art
It is known for example in U.S. Pat. No. 3,245,532 (Quinn) to provide an inspection apparatus for detecting an uneveness in the surface of an article in which beams of light are directed on separate portions of the surface of the article and the amount of light transmitted from the container is detected. U.S. Pat. No. 2,750,519 (Summerhayes et. al.) describes a method for inspecting the interior surfaces of open ended containers by means of radiant energy.
U.S. Pat. No. 2,593,127 (Fedorchak) also describes apparatus for inspecting the inner surface of a glass container by means of a light source and reflectors. Unfortunately thse and other apparatus known already suffer from major disadvantages.
Firstly, no attempt has been made in any of these known constructions of inspection apparatus to correct for variations in ambient light which would inevitably distort the response of the apparatus. Further, the quantity of light transmitted through for example, a bottle will vary between the bottom of the bottle, the neck of the bottle and the shoulder of the bottle. Thus if one measures the amount of light transmitted through the container and rejects the container when the amount of light transmitted is below a fixed amount it is possible not to detect cracks or occlusions. Further, it will be appreciated that in the case of an inspection apparatus designed to handle containers made from colored glass some provision must be made to compensate for the variations in overall light transmission which will occur from one container to the next due firstly, to variations in the color density from container to container and secondly due to variations in wall thickness from one container to another.